This invention relates to a magnetic medium, such as a thin film magnetic recording medium, and the method of manufacturing the medium. The invention has particular applicability to a magnetic recording medium exhibiting low noise, high coercivity and suitable for high-density longitudinal and perpendicular recording.
Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk.
Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. This objective becomes particularly significant as the areal recording density increases. The areal density (Mbits/in2) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times the linear density (BPI) in terms of bits per inch.
A conventional longitudinal recording disk medium is depicted in FIG. 1 and typically comprises a non-magnetic substrate 10 having sequentially deposited on each side thereof an underlayer 11, 11xe2x80x2, such as chromium (Cr) or Cr-alloy, a magnetic layer 12, 12xe2x80x2, typically comprising a cobalt (Co)-base alloy, and a protective overcoat 13, 13xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 11, 11xe2x80x2, magnetic layer 12, 12xe2x80x2, and protective overcoat 13, 13xe2x80x2, are typically deposited by sputtering techniques. A conventional overcoat layer is a carbon coating of 100-300 xc3x85. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in FIG. 1, but does not comprise Cr-containing underlayers.
The increasing demands for higher areal recording density impose increasingly greater demands on flying the head lower because the output voltage of a disk drive (or the readback signal of a reader head in disk drive) is proportional to 1/exp(HMS), where HMS is the space between the head and the media However, as the space between the head the media is decreased, the probability of head-media contacts increases and a charge buildup that occurs on the surface of the top surface of the media increases. The current recording sensor designs, AMR, GMR and spin-valve pose a very serious requirement on the ESD, electrical static discharge properties. It has been found that incorporating nitrogen in carbon thin film increases its hardness and electrical conductivity. However, it has also been found that nitrogen possesses the ability to destabilize Co hexagonal-closed packed (HCP) structure and enables more face-centered cubic (FCC) structure of the Co in the magnetic layer, imposing a detrimental and unwanted effects on the magnetic layer. Therefore, there exists a need for technology preventing the charge buildup on the top surface of the media while preventing other detrimental effects on the magnetic layer.
It has been found that the charge buildup on the top surface of the media can be reduced by decreasing the total thickness of the layers interposed between the overcoat and the magnetic layer and by using an overcoat containing nitrogen instead of the conventional carbon coating. Applicants, however, found that nitrogen from the nitrogen-containing overcoat migrates to the magnetic layer. Applicants also observed that the presence of nitrogen in carbon overcoat xe2x80x9cpoisonsxe2x80x9d the Co-alloy containing magnetic layer through destabilization of the HCP structure of the Co-alloy. Therefore, applicants recognized that there is a need to find sealing layers to be interposed between the magnetic layer and nitrogen-containing overcoat, which enhance magnetic recording performances, reduce nitrogen migration, and have good adhesion to the magnetic layer and the overcoat. This invention provides a structure and a method to prevent charge buildup on the top surface of the media by using a structure comprising a combination of a nitrogen-containing overcoat and a sealing layer comprising TiW interposed between the overcoat and the magnetic layer, wherein the sealing layer substantially prevents migration of nitrogen from the overcoat to the magnetic layer.
The present invention is a magnetic recording medium comprising an overcoat containing nitrogen that does not significantly migrate to the magnetic layer and destabilize Co HCP structure. In one embodiment, the overcoat comprises a carbon-nitrogen coating.
Another advantage of the present invention is a method of manufacturing a magnetic recording medium comprising an overcoat containing nitrogen that does not significantly migrate to the magnetic layer.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a magnetic recording medium comprising longitudinal or perpendicular magnetic recording medium comprising a magnetic layer, a sealing layer comprising TiW on the magnetic layer and an overcoat comprising nitrogen on the sealing layer, wherein the sealing layer substantially prevents migration of nitrogen from the overcoat to the magnetic layer.
Another embodiment of this invention is a longitudinal or perpendicular magnetic recording medium comprising a magnetic layer, an overcoat comprising nitrogen and a sealing means for substantially preventing migration of nitrogen from the overcoat to the magnetic layer. Embodiments of the sealing means include a sputter deposited layer of a sealing material such as TiW, preferably amorphous TiW, that substantially prevents the migration of nitrogen from the nitrogen-containing overcoat to the magnetic layer.
The sealing layer or the sealing means can substantially prevent the migration of nitrogen from the nitrogen-containing overcoat by limiting nitrogen ions migrating from the overcoat to the magnetic layer to an intensity of 1010 atoms/cm2 or less during the lifetime of the recording medium when the thickness of the layers between the magnetic layer and the overcoat is 1000 xc3x85 or less. In a preferred embodiment, the thickness of the layers between the magnetic layer and the overcoat is 750 xc3x85 or less. In a more preferred embodiment, the thickness of the between the magnetic layer and the overcoat is 500 xc3x85 or less.
Another aspect of the present invention is a method comprising sputter depositing a magnetic layer on a substrate, sputter depositing a sealing layer comprising TiW on the magnetic layer and sputter depositing an overcoat comprising nitrogen on the sealing layer, wherein the sealing layer substantially prevents migration of nitrogen from the overcoat to the magnetic layer. The substrates may be an Al-containing support, e.g., Al or Alxe2x80x94Mg, or made of glass or glass-ceramic materials.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. The drawings and description are to be regarded as illustrative in nature, and not as restrictive.